Roasted coffee beans release carbon dioxide gas by nature, so that if the roasted coffee beans are filled in a container for storage, the released carbon dioxide gas raises the inner pressure of the container, which in some cases causes deformation of the container or the like. Thus, it is necessary to fill the roasted coffee beans into the container after the carbon dioxide gas release rate is lowered or to use a container equipped with a venting mechanism in order to suppress a rise in the inner pressure of the container. In such cases, however, the aroma components of the coffee beans will be released together with the carbon dioxide gas, so that the more carbon dioxide gas is released, the less impressive the flavor of the coffee becomes.
Patent Document 1 discloses a coffee bean container incorporated with a lid that can solve the above problem. Where the pressure balance of carbon dioxide gas released from roasted coffee beans is 0.25-0.35 MPa, the container of Patent Document 1 is designed to withstand an inner pressure greater than 0.25-0.35 MPa, and therefore the container does not deform even if filled with roasted coffee beans and sealed tightly, and once the inner pressure of the container has reached 0.25-0.35 MPa, release of the carbon dioxide gas and the aroma ingredients from the container can be suppressed.
By the way, the container of Patent Document 1 has a mouth section (an opening portion) sealed with a screw cap. This screw cap is firmly screwed onto the mouth section of the container for tight sealing, so that a consumer of the coffee beans (a user of the container) needs a relatively strong grasping power or arm power to loosen the screw cap. If cap openers disclosed in Patent Documents 2 and 3 are used, even a user with a weak arm power can open the cap. However, there is a risk that if the user loosens the screw cap of the container when the inner pressure is higher than the outside pressure, the contents might blow out.